The peroxisome proliferator-activated receptors (PPARs) are transducer proteins belonging to the steroid/thyroid/retinoid receptor superfamily. The PPARs were originally identified as orphan receptors, without known ligands, but were named for their ability to mediate the pleiotropic effects of fatty acid peroxisome proliferators. These receptors function as ligand-regulated transcription factors that control the expression of target genes by binding to their responsive DNA sequence as heterodimers with the retinoid X receptor (“RXR”). The target genes encode enzymes involved in lipid metabolism and differentiation of adipocytes. Accordingly, the discovery of transcription factors involved in controlling lipid metabolism has provided insight into regulation of energy homeostasis in vertebrates, and further provided targets for the development of therapeutic agents for disorders such as obesity, diabetes and dyslipidemia.
Peroxisome proliferator-activated receptor γ(“PPARγ”) is one member of the nuclear receptor superfamily of ligand-activated transcription factors and has been shown to be expressed in an adipose tissue-specific manner. Its expression is induced early during the course of differentiation of several preadipocyte cell lines. Additional research has now demonstrated that PPARγ plays a pivotal role in the adipogenic signaling cascade. PPARγ also regulates the ob/leptin gene which is involved in regulating energy homeostasis and adipocyte differentiation, which has been shown to be a critical step to be targeted for anti-obesity and diabetic conditions.
In view of the clinical importance of PPARγ, compounds that modulate PPARγ function can be used for the development of new therapeutic agents. Potent modulators of PPARγ have been described, for example, in international patent publication no. WO 01/00579 (corresponding to U.S. application Ser. No. 09/606,433), U.S. Patent Publication No. US 2002/0037928 A1 and U.S. Pat. No. 6,200,995 B1 and U.S. Pat. No. 6,583,157 B2. One of these promising modulators, identified herein as compound 101, is in clinical development for diagnosis or therapeutic treatment of type II diabetes. Development of the modulator could yield an oral therapy to treat this illness.
Each pharmaceutical compound has an optimal therapeutic blood concentration and a lethal concentration. The bioavailability of the compound determines the dosage strength in the drug formulation necessary to obtain the ideal blood level. If the drug can crystallize as two or more polymorphs differing in bioavailability, the optimal dose will depend on the polymorph present in the formulation. Some drugs show a narrow margin between therapeutic and lethal concentrations. Chloramphenicol-3-palmitate (CAPP), for example, is a broad-spectrum antibiotic known to crystallize in at least three polymorphic forms and one amorphous form. The most stable form, A, is marketed. The difference in bioactivity between this polymorph and another form, B, is a factor of eight, thus creating the possibility of fatal overdosages of the compound if unwittingly administered as form B due to alterations during processing and/or storage. Therefore, regulatory agencies, such as the United States Food and Drug Administration, have begun to place tight controls on the polymorphic content of the active component in solid dosage forms. In general, for drugs that exist in polymorphic forms, if anything other than the pure, thermodynamically preferred polymorph is to be marketed, the regulatory agency may require batch-by-batch monitoring. Thus, it becomes important for both medical and commercial reasons to produce and market the pure drug in its most thermodynamically stable polymorph, substantially free of other kinetically favored polymorphs.
New forms of such modulators can further the development of formulations for the treatment of illnesses such as type II diabetes. For instance, salt forms of a compound, and polymorphic forms of the salt, are known in the pharmaceutical art to affect, for example, the solubility, dissolution rate, bioavailability, chemical and physical stability, flowability, fractability, and compressibility of the compound as well as the safety and efficacy of drug products based on the compound (see, e.g., Knapman, K. Modern Drug Discoveries, 2000: 53).
Accordingly, identification of a salt form or free base of the modulators with optimal physical and chemical properties will advance the development of such PPARγ modulators as pharmaceuticals. The most useful of such physical and chemical properties include: easy and reproducible preparation, crystallinity, non-hygroscopicity, aqueous solubility, stability to visible and ultraviolet light, low rate of degradation under accelerated stability conditions of temperature and humidity, low rate of isomerization of between isomeric forms, and safety for long-term administration to humans.
The free base and certain pharmaceutically acceptable salts of compound 101 are described in U.S. application Ser. No. 09/606,433, corresponding to international patent publication no. WO01/00579, and U.S. Pat. No. 6,583,157 B2. The pharmaceutically acceptable acid salts listed in these patents include, among others, those derived from inorganic acids like hydrochloric, hydrobromic, nitric, carbonic, monohydrogencarbonic, phosphoric, monohydrogenphosphoric, dihydrogenphosphoric, sulfuric, monohydrogensulfuric, hydriodic, or phosphorous acids, and the salts derived from relatively nontoxic organic acids like acetic, propionic, isobutyric, oxalic, maleic, malonic, benzoic, succinic, suberic, fumaric, mandelic, phthalic, benzenesulfonic, p-toluenesulfonic, citric, tartaric, and methanesulfonic. There is no teaching or suggestion that any of the described salt forms of the above structure are superior to the others.
We have discovered that not all of the salts are equally useful, as judged by the list of properties described above. Thus, the present invention addresses the need for potent PPARγ modulators and the need for improved solid state forms of PPARγ modulators for manufacturing and bioavailability.